Spying on bumblebees as they nest has revealed strange behaviour in those exposed to tiny amounts of a widely used pesticide.

Key points for pesticide and bees

Key points

Bumblebees exposed to neonicotinoid insecticide spent less time nursing

Research adds to the case that widely used pesticide adversely affects bees

Native bees could theoretically be at greater risk than honey bees, but experts say more research is needed

A study published in the journal Science found bees exposed to an insecticide called imidacloprid were less likely to feed and care for their larvae, and spent more time hanging out around the edges of the nest.

According to study lead author and Harvard University biologist James Crall, the most surprising and puzzling finding was that the effect on bee behaviour was strongest at night.

"If you look overnight, it's totally striking," Dr Crall said.

"Oftentimes the majority or all of a colony [affected by imidaclorprid] will be immobile — which you never see in healthy colonies.

"That means less nursing overnight."

Imidacloprid belongs to a class of insecticides called neonicotinoids (also called "neonics", which is a lot easier to say).

Chemically similar to nicotine, these are highly effective insecticides that interfere with an insect's nervous system.

There has been an ongoing and bitter dispute over the evidence that neonic use affects bees badly in the field.

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The bees were allowed to forage in adjacent chambers, some of which contained pesticide-laden nectar.

Separate to their lab study, Dr Crall and team also studied how the pesticide affected colonies in the field.

Normally, bumblebees build an insulating wax "canopy" to keep their brood protected from the cold.

But bees exposed to imidacloprid were less likely to construct canopies compared to their healthy counterparts, and were less able to control the nest's temperature.

'Unprecedented detail' in study

An Australian expert who also studies the impact of neonics on bees said the study provided unprecedented detail.

"This is the first time that we've used this method to look at the effect of a compound like this inside the colony on brood rearing," Andrew Barron of Macquarie University — and who was not involved in the new research — said.

Dr Hogendoorn said there is little research on our native bees, so we don't know whether numbers are increasing or decreasing.

"We have about 2,000 species of native bees in Australia, but we don't even know them all yet."

But Dr Hogendoorn also said studies in the US and Europe have shown native bee populations have halved. Similar figures are likely in agricultural areas in Australia due to the removal of native vegetation, as well as pesticide use.

Over half of native bee species don't forage on introduced plants, which means native bees in agricultural areas are at risk of malnutrition, Dr Hogendoorn said.

And while beekeepers can move their honey bee hives to avoid pesticide exposure, unmanaged native bees that nest in trees are more vulnerable.

"Native bees forage about 300 metres around their nest, so unlike honey bees, they cannot dilute the effects of pesticides by foraging far and wide," Dr Hogendoorn said.

Many native bees nest in trees and could be at great risk of accidental pesticide exposure, researchers say.

This would make it "more likely that a small behavioural change as a result of pesticide exposure might have a measurable impact on their ability to produce as many high quality offspring".

Where to now for neonics?

Despite concern by beekeepers and others in Australia, the Australian Pesticides and Veterinary Medicines Authority (APVMA) has no plans to review the insecticide's use in the wake of the European ban decision.

"Given that Australian honey bee health is good, there is no cause for similar restrictions here," the regulator states on its website, although it will continue to monitor the issue.

The APVMA also states that the National Residue Survey, which tests animal and plant products, has found no traces of neonics in any honey products tested.

But Dr Barron says his own research with CSIRO has found negative impacts on bees from neonics at just five parts per billion.

This is well below the 10 parts per billion level tested for by the National Residue Survey.

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